The present invention relates to temperature control apparatus which includes cascaded Peltier units, especially such apparatus wherein the Peltiers are controlled for improved thermal response time to stabilize specimen temperatures at set points over a wide temperature range. Temperature control apparatus must be included in analytical instruments when the analyzed parameter varies with the temperature of the test specimen. Although the range over which the specimen temperature must be varied by such control apparatus depends on the particular type of analysis, the analytical capability of instruments is limited by the temperature control apparatus where rapid analysis is required over a wide temperature range or where a great number of specimens must be individually analyzed in minimized time durations.
Use of the thermoelictric module or Peltier unit to both supply and remove heat has revolutionized the art of temperature control apparatus in analytical instruments by doing away with the circulating water baths that were previously necessary. However, thermal lags existing between the test specimen and the Peltier units in state of the art temperature control apparatus greatly limit the capability of analytical instruments because the thermal response time for arriving at a temperature set point can only be improved by increasing the temperature gradient to reduce these thermal lags, but when the temperature set point is reached an overshoot then occurs in proportion to the temperature gradient imposed to reach that set point. Although cascaded Peltier arrangements are commonly known in which the overall thermal difference is broken up into segments, the temperature gradient across each segment is often derived from structural characteristics or from fixed temperature set points in all such arrangements. Therefore, a compromise must be made as to the temperature gradient that acts against the thermal lag of each segment and the minimum temperature stabilization response time is limited by this compromise.